Method for Manufacturing a Surface and Integrated Circuit Using Variable Shaped Beam Lithography

ABSTRACT

A method is disclosed in which a plurality of variable shaped beam (VSB) shots is used to form a desired pattern on a surface. Shots within the plurality of shots are allowed to overlap each other. Dosages of the shots may also be allowed to vary. The union of the plurality of shots may deviate from the desired pattern. The plurality of shots may be determined such that a pattern on the surface calculated from the plurality of shots is within a predetermined tolerance of the desired pattern. In some embodiments, an optimization technique may be used to minimize shot count. In other embodiments, the plurality of shots may be optionally selected from one or more pre-computed VSB shots or groups of VSB shots. The method of the present disclosure may be used, for example, in the process of manufacturing an integrated circuit by optical lithography using a reticle, or in the process of manufacturing an integrated circuit using direct write.

RELATED APPLICATIONS

This application: 1) is a continuation-in-part of U.S. patentapplication Ser. No. 12/202,364 filed on Sep. 1, 2008 entitled “Methodand System for Manufacturing a Reticle Using Character ProjectionLithography”; 2) claims priority to U.S. Provisional Patent ApplicationSer. No. 61/172,659, filed on April 24, 2009 and entitled “Method forManufacturing a Surface and Integrated Circuit Using Variable ShapedBeam Lithography”; 3) is related to Fujimura, U.S. patent applicationSer. No. ______, entitled “Method for Optical Proximity Correction of aReticle to Be Manufactured Using Variable Shaped Beam Lithography,”(Attorney Docket No. D2SiP015CIP) filed on even date herewith; and 4) isrelated to Fujimura, U.S. patent application Ser. No. ______, entitled“Method and System for Design of a Reticle to Be Manufactured UsingVariable Shaped Beam Lithography,” (Attorney Docket No. D2SiP016CIP)filed on even date herewith; all of which are hereby incorporated byreference for all purposes.

BACKGROUND OF THE DISCLOSURE

The present disclosure is related to lithography, and more particularlyto the design and manufacture of a surface which may be a reticle, awafer, or any other surface, using variable shaped beam (VSB) chargedparticle beam lithography.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, optical lithography may be used to fabricate thesemiconductor devices. Optical lithography is a printing process inwhich a lithographic mask manufactured from a reticle is used totransfer patterns to a substrate such as a semiconductor or siliconwafer to create the integrated circuit. Other substrates could includeflat panel displays or even other reticles. Also, extreme ultraviolet(EUV) or X-ray lithography are considered types of optical lithography.The reticle or multiple reticles may contain a circuit patterncorresponding to an individual layer of the integrated circuit, and thispattern can be imaged onto a certain area on the substrate that has beencoated with a layer of radiation-sensitive material known as photoresistor resist. Once the patterned layer is transferred the layer may undergovarious other processes such as etching, ion-implantation (doping),metallization, oxidation, and polishing. These processes are employed tofinish an individual layer in the substrate. If several layers arerequired, then the whole process or variations thereof will be repeatedfor each new layer. Eventually, a combination of multiples of devices orintegrated circuits will be present on the substrate. These integratedcircuits may then be separated from one another by dicing or sawing andthen may be mounted into individual packages. In the more general case,the patterns on the substrate may be used to define artifacts such asdisplay pixels or magnetic recording heads.

In the production or manufacturing of semiconductor devices, such asintegrated circuits, maskless direct write may also be used to fabricatethe semiconductor devices. Maskless direct write or charged particlebeam lithography is a printing process in which patterns are transferredto a substrate such as a semiconductor or silicon wafer to create theintegrated circuit. Other substrates could include flat panel displays,imprint masks for nano-imprinting, or even reticles. Desired patterns ofa layer are written directly on the surface, which in this case is alsothe substrate. Once the patterned layer is transferred the layer mayundergo various other processes such as etching, ion-implantation(doping), metallization, oxidation, and polishing. These processes areemployed to finish an individual layer in the substrate. If severallayers are required, then the whole process or variations thereof willbe repeated for each new layer. Some of the layers may be written usingoptical lithography while others may be written using maskless directwrite to fabricate the same substrate. Eventually, a combination ofmultiples of devices or integrated circuits will be present on thesubstrate. These integrated circuits are then separated from one anotherby dicing or sawing and then mounted into individual packages. In themore general case, the patterns on the surface may be used to defineartifacts such as display pixels or magnetic recording heads.

As indicated, in optical lithography the lithographic mask or reticlecomprises geometric patterns corresponding to the circuit components tobe integrated onto a substrate. The patterns used to manufacture thereticle may be generated utilizing computer-aided design (CAD) softwareor programs. In designing the patterns the CAD program may follow a setof predetermined design rules in order to create the reticle. Theserules are set by processing, design, and end-use limitations. An exampleof an end-use limitation is defining the geometry of a transistor in away in which it cannot sufficiently operate at the required supplyvoltage. In particular, design rules can define the space tolerancebetween circuit devices or interconnect lines. The design rules are, forexample, used to ensure that the circuit devices or lines do notinteract with one another in an undesirable manner. For example, thedesign rules are used so that lines do not get too close to each otherin a way that may cause a short circuit. The design rule limitationsreflect, among other things, the smallest dimensions that can bereliably fabricated. When referring to these small dimensions, oneusually introduces the concept of a critical dimension. These are, forinstance, defined as the smallest width of a line or the smallest spacebetween two lines, those dimensions requiring exquisite control.

One goal in integrated circuit fabrication by optical lithography is toreproduce the original circuit design on the substrate by use of thereticle. Integrated circuit fabricators are always attempting to use thesemiconductor wafer real estate as efficiently as possible. Engineerskeep shrinking the size of the circuits to allow the integrated circuitsto contain more circuit elements and to use less power. As the size ofan integrated circuit critical dimension is reduced and its circuitdensity increases, the critical dimensions of its corresponding maskpattern approaches the resolution limit of the optical exposure toolused in optical lithography. As the critical dimensions of the circuitpattern become smaller and approach the resolution value of the exposuretool, the accurate transcription between the mask pattern and the actualcircuit pattern developed on the resist layer becomes difficult. Tofurther the use of optical lithography to transfer patterns havingfeatures that are smaller than the light wavelength used in the opticallithography process, a process known as optical proximity correction(OPC) has been developed. OPC alters the original mask pattern tocompensate for distortions caused by effects such as optical diffractionand the optical interaction of features with proximate features. OPCincludes all resolution enhancement technologies performed with areticle.

OPC adds sub-resolution lithographic features to mask patterns to reducedifferences between the original mask pattern, that is, the design, andthe final transferred circuit pattern on the substrate. Thesub-resolution lithographic features interact with the original maskpattern and with each other and compensate for proximity effects toimprove the final transferred circuit pattern. One feature that is usedto improve the transfer of the pattern is a sub-resolution assistfeature (SRAF). Another feature that is added to improve patterntransference is referred to as “serifs”. Serifs are small features thatcan be positioned on a corner of a pattern to sharpen the corner in thefinal transferred image. As the limits of optical lithography are beingextended far into the sub-wavelength regime, the OPC features must bemade more and more complex in order to compensate for even more subtleinteractions and effects. However, as imaging systems are pushed closerto their limits, the ability to produce reticles with sufficiently fineOPC features becomes critical. Although adding serifs or other OPCfeatures to a mask pattern is advantageous, it also substantiallyincreases the total features count in the mask pattern. For example,adding a serif to each of the corners of a square using conventionaltechniques adds eight more rectangles to a mask or reticle pattern.Adding OPC features is a very laborious task, requires costlycomputation time, and results in more expensive reticles. Not only areOPC patterns complex, but since optical proximity effects are long rangecompared to minimum line and space dimensions, the correct OPC patternsin a given location depend significantly on what other geometry is inthe neighborhood. Thus, for instance, a line end will have differentsize serifs depending on what is near it on the reticle. This is eventhough the objective might be to produce exactly the same shape on thewafer. These slight but critical variations are important and haveprevented others from being able to form reticle patterns. It isconventional to discuss the OPC-decorated patterns to be written on areticle in terms of main features, that is features that reflect thedesign before OPC decoration, and OPC features, where OPC features mightinclude serifs, jogs, and SRAF. To quantify what is meant by slightvariations, a typical slight variation in OPC decoration fromneighborhood to neighborhood might be 5% to 80% of a main feature size.Note that for clarity, variations in the design of the OPC are what isbeing referenced. Manufacturing variations, such as line-edge roughnessand corner rounding, will also be present in the actual surfacepatterns. When these OPC variations produce substantially the samepatterns on the wafer, what is meant is that the geometry on the waferis targeted to be the same within a specified error, which depends onthe details of the function that that geometry is designed to perform,e.g., a transistor or a wire. Nevertheless, typical specifications arein the 2%-50% of a main feature range. There are numerous manufacturingfactors that also cause variations, but the OPC component of thatoverall error is often in the range listed.

There are a number of technologies used for forming patterns on areticle, including using optical lithography or charged particle beamlithography. The most commonly used system is the variable shaped beam(VSB), which is a type of charged particle beam writer system, where aprecise electron beam is shaped and steered onto a resist-coated surfaceof the reticle. These shapes are simple shapes, usually limited torectangles of certain minimum and maximum sizes and with sides which areparallel to the axes of a Cartesian coordinate plane, and triangles withtheir three internal angles being 45 degrees, 45 degrees, and 90 degreesof certain minimum and maximum sizes. At pre-determined locations, dosesof electrons are shot into the resist with these simple shapes. Thetotal writing time for this type of system increases with the number ofshots. The doses or shots of electrons are conventionally designed toavoid overlap wherever possible, so as to greatly simplify calculationof how the resist on the reticle will register the pattern. As OPCfeatures become more complex, however, the division or fracturing ofpatterns into a set of non-overlapping simple shapes can result in manybillions of simple shapes, resulting in very long reticle write times.

It would be advantageous to reduce the time and expense it takes toprepare and manufacture a reticle that is used for manufacturing asubstrate. More generally, it would be advantageous to reduce the timeand expense it takes to prepare and manufacture any surface. Forexample, it is possible that a surface can have thousands of patternsthat have only slight differences among them. It is desirable to be ableto generate all of these slightly different patterns with a minimalnumber of VSB shots.

SUMMARY OF THE DISCLOSURE

A method is disclosed in which a plurality of variable shaped beam (VSB)shots is used to form a desired pattern on a surface. Shots within theplurality of shots are allowed to overlap each other. Dosages of theshots may also be allowed to vary. The union of the plurality of shotsmay deviate from the desired pattern. The plurality of shots may bedetermined such that a pattern on the surface calculated from theplurality of shots is within a predetermined tolerance of the desiredpattern. In some embodiments, an optimization technique may be used tominimize shot count. In other embodiments, the plurality of shots may beoptionally selected from one or more pre-computed VSB shots or groups ofVSB shots, that is, glyphs. The method of the present disclosure may beused, for example, in the process of manufacturing an integrated circuitby optical lithography using a reticle, or in the process ofmanufacturing an integrated circuit using direct write.

These and other advantages of the present disclosure will becomeapparent after considering the following detailed specification inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a variable shaped beam charged particle beam writersystem used to manufacture a surface;

FIG. 2 illustrates an optical lithography system;

FIG. 3A illustrates a design of a pattern to be placed on a substrate;

FIG. 3B illustrates a pattern formed in a reticle from the design shownin FIG. 3A;

FIG. 3C illustrates a pattern formed in the photoresist of a substrateusing the reticle of FIG. 3B;

FIG. 4A illustrates an optical proximity corrected version of thepattern shown in FIG. 3A;

FIG. 4B illustrates an optical proximity corrected version of thepattern shown in FIG. 4A after it is formed in the reticle;

FIG. 4C illustrates a pattern formed in the photoresist of a siliconwafer using the reticle of FIG. 4B;

FIG. 5A illustrates a design of a pattern to be formed on a substrate;

FIG. 5B illustrates the pattern of FIG. 5A formed on a surface using anormal dose;

FIG. 5C illustrates the pattern of FIG. 5A formed on a surface using aless than normal dose;

FIG. 5D illustrates the pattern of FIG. 5A formed on a surface using agreater than normal dose;

FIG. 6A illustrates a polygonal pattern to be formed on a surface;

FIG. 6B illustrates a fracturing of the pattern of FIG. 6A intooverlapping rectangles;

FIG. 6C illustrates the resultant pattern on the surface formed from theoverlapping rectangles of FIG. 6B.

FIG. 6D illustrates a fracturing of the pattern of FIG. 6A intonon-overlapping rectangles;

FIG. 7A illustrates a rectangular pattern which extends across a fieldboundary of a charged particle beam writer system;

FIG. 7B illustrates a pattern on the surface that may result fromwriting of the pattern in FIG. 7A due to imprecision in the chargedparticle beam writer system;

FIG. 7C illustrates another pattern on the surface that may result fromwriting the pattern of FIG. 7A due to imprecision in the chargedparticle beam writer system;

FIG. 7D illustrates a method of transferring the pattern of FIG. 7A tothe surface using a ghost shot;

FIG. 8A illustrates one division of a design pattern (hatched) intofields for writing by a charged particle beam writer system;

FIG. 8B illustrates another division of a design pattern (hatched) intofields for writing by a charged particle beam writer system;

FIG. 9A illustrates two overlapping VSB shots;

FIG. 9B illustrates a pattern on the surface resulting from theoverlapping VSB shots of FIG. 9A using a normal dose;

FIG. 9C illustrates a pattern on the surface resulting from theoverlapping VSB shots of FIG. 9A using higher than normal dose;

FIG. 10A illustrates a design of a square pattern;

FIG. 10B illustrates the pattern of FIG. 10A after OPC;

FIG. 10C illustrates a fracturing of the pattern of FIG. 10B intonon-overlapping rectangles;

FIG. 10D illustrates a fracturing of the pattern of FIG. 10B intooverlapping rectangles;

FIG. 10E illustrates an exemplary plurality of overlapping rectanglesaccording to the present disclosure;

FIG. 11A illustrates an embodiment of a conceptual flow diagram of howto prepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer;

FIG. 11B illustrates another embodiment of a conceptual flow diagram ofhow to prepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer;

FIG. 12 illustrates yet another conceptual flow diagram of how toprepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer;

FIG. 13 illustrates examples of glyphs;

FIG. 14 illustrates examples of parameterized glyphs;

FIG. 15 illustrates a further embodiment of a conceptual flow diagram ofhow to prepare a surface in fabricating a substrate such as anintegrated circuit on a silicon wafer;

FIG. 16A illustrates a pattern to be formed on a surface;

FIG. 16B illustrates use of a main VSB shot and auxiliary VSB shots toform the pattern of FIG. 16A;

FIG. 17A illustrates a pattern to be formed on a surface;

FIG. 17B illustrates use of a main VSB shot and auxiliary VSB shots toform the pattern of FIG. 17A;

FIG. 17C illustrates the resultant pattern from the shots of FIG. 17B;

FIG. 18A illustrates two VSB shots in close proximity to each other;

FIG. 18B illustrates a graph of the dose along a line drawn through theshapes of FIG. 18A;

FIG. 18C illustrates the resultant pattern on the surface from the shotsof FIG. 18A;

FIG. 19A illustrates a pattern to be formed on a surface;

FIG. 19B illustrates a curvilinear pattern which is the result of OPCprocessing on the pattern of FIG. 19A;

FIG. 19C illustrates an exemplary set of overlapping VSB shots which canform the curvilinear pattern of FIG. 19B on the surface;

FIG. 19D illustrates another exemplary set of overlapping VSB shotswhich can form the curvilinear pattern of FIG. 19B on the surface; and

FIG. 20 illustrates an embodiment of a VSB shot fracturing conceptualflow diagram.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The improvements and advantages of the present disclosure can beaccomplished by allowing overlapping VSB shots and other-than-normaldosages, and by allowing the union of the shots to deviate from thetarget pattern, allowing patterns to be created from a reduced number ofshots compared to the more conventional non-overlapping, normal dosageVSB shots. Thus, a method and a system are provided for manufacturing asurface that addresses the prior problem such as lengthy write time andconsequent high cost associated with preparing a surface.

Referring now to the drawings, wherein like numbers refer to like items,FIG. 1 identifies an embodiment of a lithography system, such as acharged particle beam writer system, in this case an electron beamwriter system 10, that employs a variable shaped beam (VSB) tomanufacture a surface 12 according to the present disclosure. Theelectron beam writer system 10 has an electron beam source 14 thatprojects an electron beam 16 toward an aperture plate 18. The plate 18has an aperture 20 formed therein which allows the electron beam 16 topass. Once the electron beam 16 passes through the aperture 20 it isdirected or deflected by a system of lenses (not shown) as electron beam22 toward another rectangular aperture plate or stencil mask 24. Thestencil mask 24 has formed therein a number of apertures 26 that definevarious simple shapes such as rectangles and triangles. Each aperture 26formed in the stencil mask 24 may be used to form a pattern in thesurface 12. An electron beam 30 emerges from one of the apertures 26 andis directed onto the surface 12 as a pattern 28. The surface 12 iscoated with resist (not shown) which reacts with the electron beam 30.The electron beam 22 may be directed to overlap a variable portion of anaperture 26, affecting the size and shape of the pattern 28. The surface12 is mounted on a movable platform 32. The platform 32 allows surface12 to be repositioned so that patterns which are larger than the maximumdeflection capability or field size of the charged particle beam 30 maybe written to surface 12. In one embodiment the surface 12 may be areticle. In this embodiment, the reticle, after being exposed with thepattern, undergoes various manufacturing steps through which it becomesa lithographic mask. The mask may then be used in an optical lithographydevice or machine 34, illustrated in FIG. 2. The optical lithographymachine 34 comprises an illumination source 36, the mask 37, and one ormore lenses 38 which project an image of the reticle pattern 28,generally reduced in size, onto a silicon wafer 39 to produce anintegrated circuit. More generally, the mask 37 is used in anotherdevice or machine to transfer the pattern 28 on to a substrate 39. Inanother embodiment the surface 12 is a substrate such as a siliconwafer.

As indicated above, since semiconductor and other nano-technologymanufacturers are reaching the limits of optical lithography, it isdifficult to transfer an ideal pattern onto a substrate. For example,FIG. 3A illustrates an ideal pattern 40, which represents a circuit, tobe formed in the resist of a substrate. When a reticle and mask areproduced that attempt to have the pattern 40 formed thereon, the reticleis not a perfect representation of the pattern 40. A pattern 42 that maybe formed in a reticle that attempts to represent the pattern 40 isshown in FIG. 3B. The pattern 42 has more rounded and shortened featuresas compared to the pattern 40. When the pattern 42 is employed in theoptical lithography process, a pattern 44 is formed in the photoresiston the substrate as depicted in FIG. 3C. The pattern 44 is not veryclose to the ideal pattern 40, demonstrating why optical proximitycorrection is required.

In an effort to compensate for the difference between the patterns 40and 44, optical proximity correction is used. Optical proximitycorrection alters the design pattern so as to alter the reticle tocompensate for distortions created by optical diffraction, opticalinteractions with neighboring shapes, and resist process effects. FIGS.4A-4C show how optical proximity correction can be employed to enhancethe optical lithography process to develop a better version of thepattern 44. In particular, FIG. 4A illustrates a pattern 50 that is analtered version of the pattern 40. The pattern 50 has a serif element 52added to various corners of the pattern 50 to provide extra area in anattempt to reduce optical and processing effects that reduce thesharpness of the corner. When a reticle of the pattern 50 is produced itmay appear in the reticle as a pattern 54 as shown in FIG. 4B. When theoptical proximity corrected pattern 54 is used in an optical lithographydevice an output pattern 56, as depicted in FIG. 4C, is produced. Thepattern 56 more resembles the ideal pattern 40 than the pattern 44 andthis is due to optical proximity correction. Although using opticalproximity correction is helpful, it may require that every pattern bealtered or decorated which increases the time and cost to produce areticle. Also, the various patterns formed on the reticle may properlyhave slight differences between them when OPC is applied and this addsto the time and expense in preparing a reticle.

Referring to FIG. 1, when a pattern is written to a resist-coatedsurface 12, the resulting pattern on the surface depends on the quantityof particles which reach the resist, called the exposure or dose. A doseof a variable shaped beam shot is the shutter speed, the length of timefor which a given shot is being projected on the surface. “Dosecorrection” is a process step in which the dose amount for any givenshot is modified slightly, for example, for proximity effect correction(PEC). Because of this the optimal or “normal” dose will not be the samefor all shots. FIG. 5A illustrates a sample polygonal pattern 60 that isto be written on a surface. FIG. 5B illustrates a pattern 62 that willresult on the reticle with a normal dose. Note that the corners ofpattern 62 are somewhat rounded compared to the ideal pattern 60. FIG.5C illustrates a pattern 64 that may result on the reticle with a lessthan normal dose. The pattern 64 is generally thinner and the long endsof the pattern are shortened somewhat compared to normal dose pattern62. FIG. 5D illustrates a pattern 66 that may result on the reticle witha greater than normal dose. The pattern 66 is “fatter”, slightly largerin all dimensions than the normal dose pattern 62. The differencesbetween patterns 62, 64 and 66 are due to the response of the resist tovarying doses.

VSB shots which overlap will inherently cause dosage variations betweenthe overlapping and non-overlapping areas. For example, FIG. 6Aillustrates a design pattern 70 which must be decomposed or fracturedinto simple shapes for VSB writing. FIG. 6B illustrates one fracturingsolution, consisting of two rectangles 72 and 74. Rectangles 72 and 74are marked with interior “X” patterns for ease of identification. As canbe seen, rectangles 72 and 74 overlap in a rectangular region 75. Ifshape 70 is exposed using rectangles 72 and 74, region 75 will receive adose that is the sum of the rectangle 72 dose and the rectangle 74 dose.This may cause the exposed pattern to be “fatter” in the vicinity ofregion 75 than the designed pattern 70. FIG. 6C illustrates a pattern 76that may be formed on a surface using the fracturing of FIG. 6B. Inpattern 76 note that the interior corners 77 are significantly roundedbecause of the extra exposure in region 75. FIG. 6D illustrates analternative fracturing of pattern 70 consisting of three rectangles 78,79 and 80 which do not overlap. The fracturing of FIG. 6D isconventionally preferred because all parts of pattern 70 can receive thenormal exposure, which may provide a more faithful transfer of designpattern 70 to the surface than the fracturing of FIG. 6B.

There are certain circumstances in which VSB shots may be conventionallyoverlapped. For example, if when the pattern is prepared for exposure, apattern shape is determined to extend beyond the boundary of one fieldof the FIG. 1 electron beam 30, then the shape must be exposed inmultiple steps, where part of the pattern is exposed, the platform 32 ismoved, and another part of the pattern is exposed. FIG. 7A illustrates apattern 81 which, in this example, crosses a field boundary 82. FIG. 7Billustrates one way in which two shots 83 and 84, if shot in differentfields, may expose the surface. Due to imprecision in the ability toposition the platform 32, shots 83 and 84 are slightly misaligned inboth the vertical and horizontal directions. In the FIG. 7B example themisalignment has produced a small area of overlap. If this pattern iseventually transferred to a substrate and manufactured into anintegrated circuit, this overlap may commonly cause no problem. FIG. 7Cillustrates another possible misalignment. In FIG. 7C the horizontalmisalignment between shots 86 and 88 has created a gap between theshots. If this gap is transferred to a substrate such as a siliconwafer, the resulting integrated circuit may not function properly. Onemethod of preventing potential misalignment from causing a circuitmalfunction is illustrated in FIG. 7D where a potential gap betweenshots 90 and 92 is filled in with a small additional shot 94, called aghost shot. Ghost shots and similar techniques designed to compensatefor imprecision in the pattern writing process result in increased shotcount.

Multi-pass writing is another conventional technique in which VSB shotsare intentionally overlapped. With this technique the entire pattern isexposed once, then the entire pattern is exposed a second time. Morethan two passes may also be used. Multi-pass writing may be used toreduce non-ideal writing effects such as resist heating, resist chargingand field-to-field misalignment. FIGS. 8A-B illustrate howfield-to-field misalignment effects can be reduced. FIG. 8A illustratesa design 96, shown as the hatched area, which has been overlaid on a 5×5field grid 98. As previously described with FIG. 7, shapes which cross afield boundary will be split and exposed in multiple steps. FIG. 8Billustrates the same design 96, shown as the hatched area, overlaid on a5×5 field grid 100 such that that the alignment of the design 96 withgrid 100 is different than with grid 98. If the patterns in the design96 are fractured for exposure on grid 98 in one pass, and thenre-fractured for exposure on grid 100 in a second pass, field-to-fieldmisalignments from the first pass will occur at different locations thanfield-to-field misalignments from the second pass, thereby reducing theeffects of misalignment. In multi-pass writing, the dosage for each passis proportionately lower than for single-pass writing, the goal beingthat the sum of the doses for all passes will be a normal dose for allparts of the pattern. Conventionally, therefore, shot overlap within apass is avoided. Multi-pass exposure may also be used to reduce theeffects of other non-ideal writing effects such as resist heating andresist charging. Multiple pass exposure substantially increases shotcount.

FIGS. 16A-B illustrate another known technique. In FIG. 16A, shape 150is the desired pattern to be formed on the surface. FIG. 16B illustratesa set of three VSB shots that may be used to form the pattern. In thisexample, shot 151 is the shape of the desired pattern, and shots 152 and153 are auxiliary shots. Shots 152 and 153 are shot with a lower thannormal dosage, and are designed to prevent the shortening of the ends ofshape 150 during exposure and subsequent resist processing. In thetechnique of FIGS. 16A-B there is a clear distinction between the shotsfor the desired pattern and the auxiliary shots.

FIGS. 17A-C illustrate another known technique. FIG. 17A illustrates adesired pattern 160 to be formed on a surface. FIG. 17B illustrates fiveVSB shots which may be used to form the pattern. Shot 161 is the mainshot. Auxiliary shots 162, 163, 164 and 165 are completely overlapped byshot 161. The auxiliary shots, which use a significantly lower dosagethan the main shot, help reduce rounding of the corners in the patternon the surface which may otherwise occur due to limitations of theparticle beam exposure system.

The aforementioned techniques for overlapping VSB shots, including ghostshots, multi-pass writing, and auxiliary shots, have two commoncharacteristics:

-   -   The union of either all the shots or some subset of the shots,        possibly oversized or undersized, matches the target pattern.    -   All of the techniques increase the shot count compared to        single-pass non-overlapping VSB shots.        The current disclosure presents a method for generating patterns        which avoids these two characteristics. In this method:    -   Shot overlap is allowed.    -   There is in general no subset of shots which, when unioned        together, matches the target pattern, even when any of the shots        are oversized.    -   The shot count may be less, often substantially less, than the        shot count for single-pass, non-overlapping VSB.        The method of the present disclosure achieves these goals by        determining, using for example computer-based optimization        techniques, a set of possibly-overlapping VSB shots which are        calculated to form the desired pattern on the surface.        Specifically, the conventional constraint of providing a normal        dose to the resist in all parts of the pattern is eliminated.        The use of other-than-normal resist dosage, both in        non-overlapping and overlapping VSB shots, allows creation of        patterns with fewer shots than with conventional techniques. The        optimization technique depends on an accurate method, such as        particle beam simulation, to calculate the pattern which will be        registered in the resist from the other-than-normal dosages. The        computational complexity involved in the particle beam        simulation and shot optimization is high, however, when applied        to a full design. The complexity of the computations have        heretofore pushed people into using uniform normal dosage, where        particle beam simulation of the entire design is not required.

The various flows described in this disclosure may be implemented usinggeneral-purpose computers with appropriate computer software. Due to thelarge amount of calculations required, multiple computers or processorcores may also be used in parallel. In one embodiment, the computationsmay be subdivided into a plurality of 2-dimensional geometric regionsfor one or more computation-intensive steps in the flow, to supportparallel processing. In another embodiment, a special-purpose hardwaredevice, either used singly or in multiples, may be used to perform thecomputations of one or more steps with greater speed than usinggeneral-purpose computers or processor cores. The optimization andsimulation processes described in this disclosure may include iterativeprocesses of revising and recalculating possible solutions.

The shot count reduction of the current disclosure compared withconventional techniques may be particularly significant for curvilinearpatterns. For example, FIG. 9A illustrates two rectangular overlappingshots 110 and 112. FIG. 9B illustrates a pattern 114 that may begenerated on the surface from normal dose shots 110 and 112, which areshown as dotted lines in FIG. 9B. The pattern 114 would require morethan two shots if non-overlapping shots were used. In another example,FIG. 9C illustrates a pattern 116 that may be generated by shots 110 and112 with each shot having a higher than normal dose. Overall, thepattern 116 is larger than pattern 114 and is somewhat differentlyshaped. Varying the dose of one or more of the overlapping shotscomprising a pattern may be used to enhance the number of patterns canbe made available using only a small number of shots. Particle beamexposure simulation may be used to determine the pattern which will beformed on a surface from a plurality of shots, such as the patterns ofFIG. 9B and FIG. 9C. Patterns which are known to be generated by asingle VSB shot or combinations of VSB shots are called glyphs. Alibrary of glyphs may be pre-computed and made available to opticalproximity correction or mask data preparation functions. For example,the patterns 116 and 114 can be pre-computed and stored in a glyphlibrary.

One complexity of using overlapping shots is calculating resist responsefor each part of the pattern. When an area of the resist receives dosesfrom multiple shots, the doses from each of the shots must be combinedto determine the total dose. For example, FIG. 18A illustrates two VSBshot patterns 500 and 502 in close proximity. FIG. 18B illustrates thedose received along the line 503 which intersects patterns 500 and 502.In FIG. 18B the dosage registered on the resist from the VSB shot forpattern 500 is 504, and the dosage registered on the resist from the VSBshot for pattern 502 is 506. Dashed line 508 shows the threshold 508above which the resist will register the pattern. Dotted line 510illustrates the combination of 504 and 506 in the area where both 504and 506 are significant. It should be noted that the combined dose 510does not go below the resist threshold 508 at any point between thepatterns 500 and 502. The combination dose curve 510 therefore showsthat the resist will register patterns 500 and 502 as a single combinedpattern 512, as illustrated in FIG. 18C.

It is significantly more challenging to predict a resulting pattern onthe surface when areas on the resist receive significantly more or lessthan a normal dose. Particle beam exposure simulation may be used todetermine the resulting pattern. This process simulates the exposure ofthe resist-coated surface by the charged particle beam system,accounting for the physical characteristics of the charged particle beamsystem and the electro-optical and chemical characteristics of theresist and the surface underlying the resist. Particle beam exposuresimulation may be used to model various non-ideal effects of the chargedparticle beam exposure process, including forward scattering, backwardscattering, resist diffusion, coulomb effect, etching, fogging, loadingand resist charging. Most of these effects are shorter-range effects,meaning that each VSB shot will affect only other nearby parts of thepattern. Back scattering, fogging and loading, however, are longer-rangeeffects, and cannot be accurately simulated when only small parts of apattern are considered. Resist charging, although a short-range effect,must be calculated after the final shot exposure sequence is known.

For example, FIG. 20 illustrates one embodiment of a flow for generatingVSB shots for a pattern, a process called fracturing, by pre-calculatingglyphs. In the FIG. 20 flow 900, the desired pattern 902 is the patternthat is to be formed on the surface, and is the primary input to theprocess. Etch correction may be calculated in step 904, based on an etchmodel 906. Step 904 creates a desired resist pattern 908—that is thedesired pattern to be formed on the resist before etching. Desiredresist pattern 908 is therefore the target pattern for matching byglyphs. Separately, a combination of VSB shots 920 may be simulated instep 922 to create a glyph to add to the library of glyphs 926. Theparticle beam simulation step 922 uses models for one or more of theshort-range exposure effects 924. The resulting glyphs in glyph library926 are therefore pre-compensated for the short-range exposure effects.Long range exposure effects cannot be compensated for during glyphgeneration, because the range of the effects may be larger than theglyph pattern. In step 910 glyphs from the glyph library are selected,placed, and dosages assigned so as to create a pattern on the resistwhich matches the etch-corrected desired pattern 908 within apredetermined tolerance. Step 910 uses one or more of the long-rangeexposure effects 912 in determining shot dosage. The output of step 910is an initial list of VSB shots 914. The initial set of VSB shots 914may then be simulated in step 916 and further corrected or revised. Instep 917 the simulated pattern from step 916 is compared with thedesired resist pattern 908 to determine if the two patterns match withinthe predetermined tolerance. If a match within the predeterminedtolerance is not found, additional correction and simulation may be donein step 916 until the particle beam simulated pattern from step 916 iswithin the predetermined tolerance of the etch-corrected desired pattern908. The tolerance used in step 917 may also be adjusted if no matchwithin the predetermined tolerance can be achieved. The result of step917 is a verified shot list 918 which is suitable for writing to theresist-coated surface using a charged particle beam system.

FIGS. 10A-E illustrate an example of how use of overlapping shots withvarying doses can reduce shot count. FIG. 10A illustrates an idealpattern 118, such as a contact, that may be generated by an electronicdesign-automation software system, to be used with optical lithographyin forming a pattern on a substrate. The pattern 118 is in the shape ofa square. FIG. 10B illustrates a curvilinear pattern 120 that may becreated by OPC processing of pattern 118. Pattern 120 is to be formed ona reticle for use in making a mask for use an optical lithographicprocess. FIG. 10C illustrates one set 122 of non-overlapping rectangleswhich may be used to write pattern 120 on the reticle using VSBtechnology. As can be seen, the union of the set of rectangles 120closely approximates the shape 120. However, some charged particle beamsystems are relatively inaccurate when shots with high length-to-widthaspect ratios, called slivers, are shot. The set of rectangles 120 istherefore not conventionally created by fracturing software. FIG. 10Dillustrates another set of non-overlapping shapes—rectangles andtriangles—that may be conventionally used to write shape 120 to asurface. This set of shapes can be shot using VSB technology without useof slivers. There are 7 shots in shot group 124. This is a large numberof shots for a figure as simple as shape 120. FIG. 10E illustrates athree-shot group 130 of the present disclosure that can, with properdosages, register a pattern on the reticle which is close to the desiredpattern 120. In this example, shots 132 and 134 have a relative dose of1.0, and shot 136 has a relative dose of 0.6. The pattern registered onthe resist is the shape 140, which is equivalent to the desired shape120, within a pre-determined tolerance. The 3-shot group 130 canregister a pattern on the resist that is closer to the desired pattern120 than is the 7-shot group 124. This example shows how overlappingshots with varying dosages may be effectively used to reduce shot count.Patterns may be formed which are substantially different than a patternwhich would be formed by a simple union of shots. Furthermore,curvilinear shapes can be formed, even with shots which are parallel tothe axes of the Cartesian plane. The shot group 130 may be pre-computedand made available as a glyph for use with all contacts matching thecontact pattern 118.

FIGS. 19A-C illustrate overlapping VSB shots with a more complexpattern. In FIG. 19A, pattern 180 consists of two square shapes 182 and184 that, for example, may be generated by a computer-aided designsoftware system, for use in an optical lithographic process. FIG. 19Billustrates a corresponding pattern 186 that may be produced by OPCprocessing of pattern 180. This example shows that OPC processing of twoidentical shapes 182 and 184 can produce sets of resultant shapes thatare slightly different. A large number of conventional non-overlappingVSB shots would be required to form pattern 186 on a reticle. FIG. 19Cillustrates a set of overlapping variable dosage VSB shots 190 that cangenerate the curvilinear pattern 186 on a reticle. The shots in the setof VSB shots 190 have varying dosages, although the dosages are notillustrated. In determining this set of shots, a minimum shot size andmaximum shot aspect ratio have been set as constraints. Note that theunion of the shots in 190—the total area covered by the combination 190of shots—does not match the curvilinear pattern 186. Nor does any subsetof the set of VSB shots 190 match curvilinear pattern 186. Nevertheless,the calculated pattern that the resist will register does match thecurvilinear pattern 186 within a predetermined tolerance. FIG. 19Dillustrates another set of overlapping variable dosage VSB shots 194that can generate the curvilinear pattern 186 on a reticle. As with FIG.19C, the shots in the set of VSB shots 194 have varying dosages. Thelocations of the shots in the set of shots 190 and the set of shots 194are quite different, yet both sets form the pattern 186 within thepredetermined tolerance. This example shows how relatively efficientlycurvilinear patterns may be produced on the surface with the presentdisclosure.

FIG. 11A is a conceptual flow diagram 250 of an embodiment of thepresent disclosure for preparing a surface for use in fabricating asubstrate such as an integrated circuit on a silicon wafer using opticallithography. In a first step 252, a physical design, such as a physicaldesign of an integrated circuit is designed. This can includedetermining the logic gates, transistors, metal layers, and other itemsthat are required to be found in a physical design such as that in anintegrated circuit. Next, in a step 254, optical proximity correction isdetermined. In an embodiment of this disclosure this can include takingas input a library of pre-calculated glyphs or parameterized glyphs,which advantageously may reduce the computing time for performing OPC.In an embodiment of this disclosure, an OPC step 254 may also includesimultaneous optimization of shot count or write times, and may alsoinclude a fracturing operation, a shot placement operation allowingoverlapping shots, a dose assignment operation allowingother-than-normal dosages, or may also include a shot sequenceoptimization operation, or other mask data preparation operations. TheOPC step 254 may also use particle beam simulation. Once opticalproximity correction is completed, a mask design is developed in a step256. Then, in a step 258, a mask data preparation operation which mayinclude a fracturing operation, a shot placement operation, a doseassignment operation, or a shot sequence optimization may take place.Either of the steps of the OPC step 254 or of the MDP step 258, or aseparate program independent of these two steps 254 or 258 can include aprogram for determining a large number of glyphs or parameterized glyphsthat can be shot on the surface to write all or a large part of therequired patterns on a reticle. Combining OPC and any or all of thevarious operations of mask data preparation in one step is contemplatedin this disclosure. Mask data preparation (MDP) step 258 may include afracturing operation in which shot overlap and other-than-normal dosageassignment is allowed, and may also include particle beam simulation.MDP step 258 may also comprise a pattern matching operation to matchglyphs to create a mask that matches closely to the mask design. Maskdata preparation may also comprise inputting patterns to be formed on asurface with some of the patterns being slightly different, and usingparticle beam exposure simulation to calculate variation in shot dose orvariation in shot overlap to reduce the shot count or total write time.A set of slightly different patterns on the surface may be designed toproduce substantially the same pattern on a substrate. Once the maskdata preparation is completed, the surface is generated in a mask writermachine, such as an electron beam writer system. This particular step isidentified as a step 262. The electron beam writer system projects abeam of electrons through apertures in a stencil mask onto a surface toform patterns on the surface, as shown in a step 264. The completedsurface may then be used in an optical lithography machine, which isshown in a step 266. Finally, in a step 268, a substrate such as asilicon wafer is produced. The glyph generation step 274 providesinformation to a set of glyphs or parameterized glyphs in step 276. Ashas been previously described, the glyph generation step 274 may useparticle beam simulation. Also, as has been discussed, the glyphs orparameterized glyphs step 276 provides information to the OPC step 254or the MDP step 258.

FIG. 11B is a more detailed flow diagram 280 of how to prepare a surfacefor use in fabricating a substrate such as an integrated circuit on asilicon wafer, in which OPC and MDP operations are beneficially combinedin a single step. In a first step 282, a physical design, such as aphysical design of an integrated circuit is obtained. The physicaldesign may be an integrated circuit design obtained directly fromconventional CAD physical design software, or it may be created from theintegrated circuit design by performing, for example, Booleanoperations, sizing, biasing, or retargeting of one or multiple designlayers. Next, in step 284, OPC and MDP operations are performed in asingle step named Mask Data Correction (MDC). Information 296 regardingthe characteristics of the charged particle beam writer system and themask manufacturing process are supplied to the MDC step. The information296 may include, for instance, forward scattering, back scattering,resist diffusion, coulomb effect, resist charging, fogging, maximum shotsize, maximum shot aspect ratio and shot geometrical descriptions. Theinformation 296 may also include a library of possible VSB shots. Inanother embodiment a library of pre-computed or pre-calculated glyphs297 may also be supplied to the MDC step. Information 298 required toperform OPC is also supplied to the MDC step 284. The MDC step 284 usesthe available information 296 regarding the charged particle beam systemand the process when performing optical proximity effect correction 298.The MDC step 284 optimizes the generated set of VSB shots in order toachieve a desired wafer image 294. The desired wafer image, that is thetarget of the MDC step, may be the physical design 282 or may be derivedfrom the physical design 282. The optimization may include the choice ofthe VSB shots, their locations, and their doses. The choice of the VSBshots, their locations, and their doses may be based on the chargedparticle beam system information 296, on a database of VSB shots, on alibrary of glyphs, or a combination thereof. The optimization of thefractured data may include the simulation of the mask image, asimulation of the wafer image based on the simulated mask image, acomparison of the simulated wafer image and the target wafer image. Theresult of such comparison may be used as an optimization criteria. Otheroptimization criteria may also include: the number of VSB shots, theminimum size of the VSB shots (i.e. slivers), the creation of identicalsets of VSB shots for identical target wafer images in the sameenvironment, and the creation of symmetrical sets of VSB shots forwriting symmetrical patterns in the physical design 282. Next, theprepared mask layout 286 which is created by the MDC step 284 is used ina mask writer system 288 to generate patterns on a surface 290. Thecompleted surface may then be used in an optical lithography machine,which is shown in step 292. Lastly an image on a wafer is produced instep 294.

With reference now to FIG. 12, another conceptual flow diagram 300 ofhow to prepare a surface for use in fabricating a substrate such as anintegrated circuit on a silicon wafer using optical lithography isshown, in which a mask design generated from mask data preparationoutput is compared to the post-OPC mask design based on an equivalencecriteria. In a first step 302, a physical design, such as a physicaldesign of an integrated circuit is designed. This may be the idealpattern that the designer wants transferred onto a substrate. Next, in astep 304, optical proximity correction of the ideal pattern generated inthe step 302 is determined. This can include selecting glyphs that needto be prepared. Optical proximity correction may also comprise inputtingpossible glyphs, the glyphs being determined using particle beamexposure simulation to calculate varying a shot dose or varying shotoverlap. Further, optical proximity correction may comprise selecting aglyph from the possible glyphs, computing the transferred pattern on thesubstrate based on the selected glyph, and selecting another glyph ifthe computed pattern differs from the desired corrected pattern bygreater than a predetermined threshold. Once optical proximitycorrection is completed a mask design is developed in a step 304. Then,in a step 306, a mask design is prepared. Once the mask design isprepared further enhancement of the mask design takes place in a maskdata preparation step 308. Mask data preparation may also comprisepattern matching to match glyphs to create a mask that matches closelyto the mask design. Iterations, potentially including only one iterationwhere a correct-by-construction “deterministic” calculation isperformed, of pattern matching, dose assignment, and equivalencechecking may also be performed. These steps will assist in preparing anenhanced equivalent mask design.

Once the mask is enhanced, an equivalent mask design, such as a set ofVSB shots, is generated in a step 310. There are two motivations fortests that can be used to determine whether the equivalent mask designis really equivalent to the mask design. One motivation is to pass maskinspection. Another motivation is to confirm that the chip or integratedcircuit will function properly once it has been fabricated. Thecloseness to which a pattern matching operation declares a match may bedetermined by a set of equivalence criteria. An equivalence criteria maybe driven at least partially by litho-equivalence. Litho-equivalence maybe determined by a set of predetermined geometric rules, a set ofmathematical equations that declare a match, a partial match, or a nomatch, or by running a lithography simulation of the mask design and alithography simulation of the equivalent mask design and by comparingthe two results using a set of predetermined geometric rules, or by aset of mathematical equations that declare a match, a partial match, orno match. The MDP step 308 may use a pre-determined set of glyphs, orparameterized glyphs to optimize for shot count or write time whileinsuring that a resulting equivalent mask design 310 is acceptable tothe equivalence criteria. In another embodiment, OPC and MDP may becombined in a correct-by-construction method, in which case there maynot be the mask design 306 generated separately from the equivalent maskdesign 310.

Once the equivalent mask design is determined to be correct, a surfaceis prepared in a charged particle beam writer system, such as anelectron beam writer system. This step is identified as a step 314 maskwriter. The electron beam writer system projects a beam of electronsthrough apertures in a stencil mask onto a surface to form patterns onthe surface. The surface is completed in a step 316, mask image. Thecompleted surface may then be used in an optical lithography machine,which is shown in a step 318 to transfer the patterns found on thesurface to a substrate such as a silicon wafer to manufacture anintegrated circuit. Finally, in a step 320, a substrate such as asemiconductor wafer is produced. The glyph generation step 326 providesinformation to a set of glyphs or parameterized glyphs in step 328. Ashas been previously described, the glyph generation step 326 may useparticle beam simulation. Also, as has been discussed, the glyphs orparameterized glyphs step 328 provides information to either the OPCstep 304 or the MDP step 308.

Referring again to FIG. 11A, as discussed above, in one embodiment, theOPC step 254 may include various functions of the MDP step 258. Theoptical proximity correction system can start with a large library ofpre-computed or pre-calculated glyphs. The optical proximity correctionsystem can then attempt to use the available glyphs as much as possiblein performing optical proximity correction transformation of theoriginal physical design of the integrated circuit to the reticledesign. Glyphs may be each marked with an associated shot count andwrite time optimization value or values and an optical proximitycorrection system, a mask data preparation system, or some independentprogram may optimize for shot count or write time by selecting the lowershot count or write time. This optimization may be performed in a greedymanner where each glyph is chosen to optimize what is the best glyph tochoose for shot count or write time with a certain order in which tochoose glyphs to match a pattern, or in an iterative optimization mannersuch as with simulated annealing where exchanges of glyph selectionoptimizes the overall shot count or write time. It is possible that somedesired patterns to be formed on a reticle may still remain unmatched byany available glyphs and such patterns may need to be formed by use ofindividual VSB shots not part of any pre-computed glyph.

Referring now to FIG. 15, another conceptual flow diagram 700 of how toprepare a surface which is directly written on a substrate such as asilicon wafer is shown. In a first step 702, a physical design, such asa physical design of an integrated circuit is determined. This may be anideal pattern that the designer wants transferred onto a substrate.Next, in a step 704, proximity effect correction (PEC), and other datapreparation (DP) steps are performed to prepare input data to asubstrate writing device, where the result of the physical designcontains a multiplicity of patterns that are slightly different. Thestep 704 may also comprise inputting possible glyphs or parameterizedglyphs from step 724, the glyphs being based on possibly overlapping VSBshots, and the glyphs being determined using a calculation of varying ashot dose or varying a shot position in glyph generation step 722. Thestep 704 may also comprise pattern matching to match glyphs to create awafer image that matches closely to the physical design created in thestep 702. Iterations, potentially including only one iteration where acorrect-by-construction “deterministic” calculation is performed, ofpattern matching, dose assignment, and equivalence checking may also beperformed. The result of step 704 is a set of wafer writing instructions706. Wafer writing instructions 706 are then used to prepare a wafer ina wafer writer machine, such as an electron beam writer system. Thisstep is identified as the step 710. The electron beam writer systemprojects a beam of electrons through an adjustable aperture onto asurface to form patterns in a surface. The surface is completed in astep 712. The glyph generation step 722 provides information to a set ofglyphs or parameterized glyphs in step 724. The glyphs or parameterizedglyphs step 724 provides information to the PEC and Data Prep step 704.The step 710 may include repeated application as required for each layerof processing, potentially with some processed using the methodsdescribed in association with FIGS. 11A and 12, and others processedusing the methods outlined above with respect to FIG. 15, or othersproduced using any other wafer writing method to produce integratedcircuits on the silicon wafer.

Referring now to FIG. 13, examples of glyphs 1000, 1002, 1004, and 1006that may be used by optical proximity correction, fracturing, proximityeffect correction, or any other steps of mask data preparation areshown. These glyphs 1000, 1002, 1004, and 1006 may be generated by asimilarly-fractured set of VSB shots or may be generated by differentfracturings. Regardless of the method of creating the glyphs, the glyphsrepresent possible patterns that are known to be possible patterns onthe surface. Each glyph may have associated with it the position anddosage information for each of the VSB shots comprising the glyph.

FIG. 14 shows examples of parameterized glyphs 1010 and 1012. The glyph1010 demonstrates a general shape described with a specification of adimension that can be varied, in this case the length X being variedfrom length unit values between 10 and 25. The glyph 1012 demonstratesthe same general shape in a more restrictive way where the length X canonly be one of the specific values, for example, 10, 15, 20, or 25. Theparameterized glyph 1010 demonstrates that these descriptions allow fora large variety of possible glyphs that is not practical with theenumeration method of glyphs that are not parameterized.

An example of a parameterized glyph description for the glyph 1010 maybe as follows:

pglyph upsideDownLShape (x : nanometers where ((x = 10) or ((x > 10) and(x < 25)) or (x = 25))); rect (0, 0, 5, 15); rect (0, 15, x, 20); endpglyph;

An example of a parameterized glyph description for the glyph 1012 maybe as follows:

pglyph upsideDownLShape2 (x : nanometers where ((x = 10) or (x = 15) or(x = 20) or (x = 25))); rect (0, 0, 5, 15); rect (0, 15, x, 20); endpglyph;

These example descriptions are based on parameters that yield a logicaltest that determines which values of parameters meet a certain criteriasuch as “where ((x=10) or (x=15) or (x=20) or (x=25))” or “where ((x=10)or ((x>10) and (x<25)) or (x=25)).” There are many other ways todescribe a parameterized glyph. Another example that demonstrates aconstructive method is as follows:

pglyph upsideDownLShape2 (x : nanometers); glyphFor (x = 10, x + x+5;x>25) { rect (0, 0, 5, 15); rect (0, 15, x, 20); } end pglyph;.

While the specification has been described in detail with respect tospecific embodiments, it will be appreciated that those skilled in theart, upon attaining an understanding of the foregoing, may readilyconceive of alterations to, variations of, and equivalents to theseembodiments. These and other modifications and variations to the presentsystem and method for manufacturing a surface or integrated circuitusing variable shaped beam lithography may be practiced by those ofordinary skill in the art, without departing from the spirit and scopeof the present subject matter, which is more particularly set forth inthe appended claims. Furthermore, those of ordinary skill in the artwill appreciate that the foregoing description is by way of exampleonly, and is not intended to be limiting. Thus, it is intended that thepresent subject matter covers such modifications and variations as comewithin the scope of the appended claims and their equivalents.

1. A method for manufacturing a surface using charged particle beam lithography, the method comprising: inputting a desired pattern to be formed on the surface; determining a plurality of variable shaped beam (VSB) shots, wherein shots in the plurality of shots are allowed to overlap each other, and wherein the union of any subset of the plurality of VSB shots, each shot in the subset being oversized or being undersized or being the originally-determined size, is different than the desired pattern; calculating a calculated pattern on the surface from the plurality of VSB shots; revising the plurality of VSB shots and recalculating the calculated pattern if the calculated pattern differs from the desired pattern by more than a predetermined tolerance; and forming the pattern on the surface with the plurality of VSB shots.
 2. The method of claim 1 wherein the step of calculating comprises charged particle beam simulation.
 3. The method of claim 2 wherein the charged particle beam simulation includes at least one of a group consisting of forward scattering, backward scattering, resist diffusion, coulomb effect, etching, fogging, loading and resist charging.
 4. The method of claim 1 wherein the desired pattern is curvilinear.
 5. The method of claim 1 wherein each VSB shot comprises a dose, and wherein the doses of the VSB shots are allowed to vary with respect to each other.
 6. The method of claim 1 wherein at least one of the steps of determining and revising comprises using an optimization technique to determine the plurality of VSB shots.
 7. The method of claim 6 wherein the plurality of VSB shots is minimized in number.
 8. The method of claim 6 wherein the plurality of VSB shots having an aspect ratio greater than a predetermined maximum is minimized in number.
 9. The method of claim 1 further comprising inputting possible glyphs, each of the glyphs being determined using a calculation of at least one VSB shot, wherein the step of determining comprises selecting a glyph from the possible glyphs.
 10. The method of claim 1 wherein the plurality of VSB shots is constrained to be symmetrical when the desired pattern is symmetrical.
 11. The method of claim 1 wherein the surface is a reticle.
 12. The method of claim 1 wherein the surface is a substrate.
 13. The method of claim 1 wherein the step of determining uses a correct-by-construction deterministic technique.
 14. A method for manufacturing an integrated circuit using an optical lithographic process, the optical lithographic process using a reticle, the method comprising: inputting a desired pattern to be formed on the reticle; determining a plurality of variable shaped beam (VSB) shots, wherein shots in the plurality of shots are allowed to overlap each other, and wherein the union of any subset of the plurality of VSB shots, each shot in the subset being oversized or being undersized or being the originally-determined size, is different than the desired pattern; calculating a calculated pattern on the reticle from the plurality of VSB shots; revising the plurality of VSB shots and recalculating the calculated pattern if the calculated pattern differs from the desired pattern by more than a predetermined tolerance; and forming the pattern on the reticle with the plurality of VSB shots.
 15. The method of claim 14 wherein the step of calculating comprises charged particle beam simulation.
 16. The method of claim 15 wherein the charged particle beam simulation includes at least one of a group consisting of forward scattering, backward scattering, resist diffusion, coulomb effect, etching, fogging, loading and resist charging.
 17. The method of claim 14 wherein each VSB shot comprises a dose, and wherein the doses of the VSB shots are allowed to vary with respect to each other.
 18. The method of claim 14 wherein at least one of the steps of determining and revising comprises using an optimization technique to determine the plurality of VSB shots.
 19. The method of claim 18 wherein the plurality of VSB shots is minimized in number.
 20. The method of claim 14 further comprising: manufacturing a mask from the reticle, the mask containing the pattern formed on the reticle; and transferring the pattern on the mask to a substrate using optical lithography.
 21. The method of claim 20 further comprising: inputting an ideal pattern on the substrate; and calculating a simulated pattern on the substrate, wherein the step of determining comprises minimizing the difference between the ideal pattern on the substrate and the simulated pattern on the substrate.
 22. The method of claim 21, wherein the simulated pattern on the substrate is calculated using the calculated pattern on the reticle.
 23. A method for manufacturing an integrated circuit, the integrated circuit having a substrate, the method comprising: inputting a desired pattern to be formed on the substrate; determining a plurality of variable shaped beam (VSB) shots, wherein shots in the plurality of shots are allowed to overlap each other, and wherein the union of any subset of the plurality of VSB shots, each shot in the subset being oversized or being undersized or being the originally-determined size, is different than the desired pattern; calculating a calculated pattern on the substrate from the plurality of VSB shots; revising the plurality of VSB shots and recalculating the calculated pattern if the calculated pattern differs from the desired pattern by more than a predetermined tolerance; and forming the pattern on the substrate with the plurality of VSB shots.
 24. The method of claim 23 wherein the step of calculating comprises charged particle beam simulation.
 25. The method of claim 23 wherein at least one of the steps of determining and revising comprises using an optimization technique to determine the plurality of VSB shots. 